The majority of electronic equipment produced presently, and in particular computers, communication systems, military surveillance equipment, stereo and home entertainment equipment, televisions and other appliances include miniaturized components to perform new high speed functions and electrical interconnections which according to the materials from which they are made or their mere size are very susceptible to stray electrical energy created by electromagnetic interference or voltage transients occurring on electrical lines. Voltage transients can severely damage or destroy such micro-electronic components or contacts thereby rendering the electronic equipment inoperative, and requiring extensive repair and/or replacement at great cost. Based upon the foregoing there was found a need to provide a multi-functioning electronic component architecture which attenuates electromagnetic emissions resulting from differential and common mode currents flowing within electronic circuits, single lines, pairs of lines and multiple twisted pairs. Such multi-functioning electronic components are the subject of commonly owned U.S. Pat. Nos. 5,909,350, 6,097,581, and 6,018,448, all incorporated herein by reference.
While the above referenced electronic components accomplish their respective tasks, usage of such components has been limited for a number of reasons. First, the number of such components required continues to increase as applications, such as data buses, continue to grow. In addition, as the number of required components grows, so does the physical size of multi-component packages. Second, by their nature the electronic components referred to are delicate structures which do not handle physical stress well. During the manufacture of electronic products a number of mechanical stresses associated with handling and soldering can damage the components.
Another drawback to using the referenced electronic components is that it becomes very tedious to manually handle and mount the components on electronic products being assembled. This often time translates into lower product yields and added expense due to broken or misconnected components. A further disadvantage to some of the components is that they include leads for thru-hole insertion. Physical stressing, bending or applying torque to the leads can cause a failure in the final product, either immediately or later thereby affecting the products overall reliability.
Another source of electrical noise found in prior art differential mode filters, common mode filters and capacitor decouplers is caused by imperfections in the capacitors that make up the filters and decouplers. The effects of these imperfections are commonly referred to as parasitic effects. Parasitic or non-ideal capacitor behavior can manifest itself in the form of resistive and inductive elements, nonlinearity and dielectric memory. The four most common effects are leakage or parallel resistance, equivalent series resistance (ESR), equivalent series inductance (ESL) and dielectric absorption. The equivalent series resistance (ESR) of a capacitor is the resistance of the capacitor leads in series with the equivalent resistance of the capacitor plates. ESR causes the capacitor to dissipate power during high flowing ac currents. The equivalent series inductance (ESL) of a capacitor is the inductance of the capacitor leads in series with the equivalent inductance of the capacitor plates. An additional form of parasitic that goes beyond the component itself is stray capacitance which is attributed to the attachment of the capacitor element within an electrical circuit. Stray capacitors are formed when two conductors are in close proximity to each other and are not shorted together or screened by a Faraday shield. Stray capacitance usually occurs between parallel traces on a PC board or between traces/planes on opposite sides of a PC board. Stray capacitance can cause problems such as increased noise and decreased frequency response.
Several other sources of electrical noise include cross talk and ground bounce. Cross talk in most connectors or carriers is usually the result of mutual inductance between two adjacent lines rather than from parasitic capacitance and occurs when signal currents follow the path of least inductance, especially at high frequencies, and return or couple onto nearby conductors such as conductive tracks positioned parallel with or underneath the signal current track. Ground bounce is caused by shifts in the internal ground reference voltage due to output switching of a component. Ground bounce causes false signals in logic inputs when a device output switches from one state to another. It has been found that the multi-functioning electronic components, specifically the differential and common mode filters and decouplers disclosed in the above referenced, commonly owned U.S. patent applications, provide improved performance when coupled or used with an enlarged ground shield that can substantially decrease or reduce and in some cases can eliminate capacitor parasitics, stray capacitance, mutual inductive coupling between two opposing conductors, various forms of cross talk and ground bounce.
Therefore, in light of the foregoing deficiencies in the prior art, the applicant's invention is herein presented.